The mines were found this week during the navy’s mine countermeasures exercise carried out with navy teams from Japan, Australia and the United States.
The navy says 16 mines were laid in seven loops as part of a controlled defensive minefield in September 1942.
They were part of a larger defensive manoeuvre which saw 1391 mines laid in 10 New Zealand harbours.
Most of the mines were disposed of using mine sweepers after the war, but about 50 sank to the seabed.
The navy says the mines are unlikely to be dangerous due to their age and condition but recommends caution if any more are found.